It is generally recognized that there is a global requirement to use more renewable energy, rather than energy from conventional fossil fuel sources. A difficulty with the use of natural energy forms, such as wind and solar energy, is their relatively low energy concentration and variable availability. In the context of buildings there are practical issues of scale for natural energy collectors, for instance wind turbines and solar PV (photovoltaic) panels. Taking as an example a residential property with either a 3 metre diameter wind turbine or 10 square metres of solar PV panels, the average electrical energy output would typically be in the range 200-400 Watts. Assuming the building has an outer surface area of 100 square metres then the available energy would be 2-4 Watts per square metre. This being a low wattage per square metre, it is therefore desirable to utilize the energy captured by these devices as efficiently as possible. One method is the release of the electrical energy in the form of heat.
It is well known from the study of thermodynamics that heat requires a temperature gradient to cross system boundaries. In the prior art, EP-A-0 049 790 discloses a method of using large quantities of low-grade energy to heat a building. The device warms the outside of a partition wall to a temperature between the building temperature and the atmospheric temperature. A thermal gradient is formed that reduces the flow of heat from the building. An air gap is used for insulation. EP-A-0 719 976 discloses a device using a heat gradient to reduce heat flows from a thermal mass. A metal plate, typically iron, has a lamination of a thin film of typically plastic material. The reference explains the combination creates a higher temperature in the lamination than the temperature of the thermal mass. The same device is revealed in EP-A-0 716 444 as providing a cooling effect.
Many insulation materials have been developed to insulate the walls, roofs and floors of buildings. Inorganic materials such as mineral fibres are in widespread use, as are organic materials such as foams. Typically these insulation materials are placed in buildings in a position adjacent to the outside surfaces of the structure. Generally the insulation layers are not in an airtight enclosure and are therefore indirectly exposed to moisture in the atmosphere. Indeed some materials may be intentionally exposed to the atmosphere using a technique described as ‘breathing wall’. Under the circumstances described, temperature variations between the insulation enclosure and the atmosphere outside may cause condensation. This is more probable in the winter period during the time the thermal insulation properties are most required.
One disadvantage of this atmospheric exposure is that most insulation materials exhibit some hygroscopic tendencies. The absorption of water has a detrimental effect on the thermal insulation value of the material. For instance a dry mineral fibre with a thermal efficiency in terms of U value of 0.4 Watts per square metre per degree Kelvin may have a U value of 0.8 Watts per square metre per degree Kelvin at a 10% moisture content. Similarly a dry polyurethane foam with a U value of 0.3 Watts per square metre per degree Kelvin may have a U value of 0.4 Watts per square metre per degree Kelvin at a 10% moisture content. This represents a reduction in thermal performance that can be allowed for by increasing the thickness of the insulation material. In terms of constructing a building this creates problems of the increased space required for the insulation and the material cost. Generally insulation manufacturers provide moisture barriers as a method of reducing moisture absorption. Another problem is the effect of moisture absorption on the lifespan of insulation materials. It is well know that moisture ingress over time is an important factor in the deterioration of buildings. Most insulation materials have relatively short durability data, measured in terms of decades rather than the expected one hundred year life of a building.
Manufacturers of insulation products are supplying high efficiency insulation with U values typically in the range 0.01 to 0.02 Watts per square metre per degree Kelvin.
Utilizing an energy supply, providing low Wattages per square metre of building surface area, for heating applications is relatively difficult. In addition thermal insulation materials for buildings would operate at higher thermal efficiencies with the provision of a heat source to provide resistance to moisture absorption.
An aim of the present invention is to improve the thermal insulation of buildings by utilizing a neutral thermal gradient. A further aim is to maintain the thermal efficiency and integrity of the insulating material by controlling moisture absorption.